Antiluteinizing Hormone: Chronic Influence on Steroid and Gonadotropin Levels and Superovulation in the Pregnant Hamster*

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Abstract
Pregnant hamsters were injected with either normal horse serum (NHS) or equine antibovine LH (ALH) and autopsied 4 days later (day 1 of pregnancy = sperm positive). Pregnancy was interrupted by a single sc injection of 0.1 ml ALH on days 4, 8, or 10. On days 6 and 12, 0.2 ml ALH was needed to interrupt pregnancy; however, ALH was only partially effective on day 12. After ALH on days 4 or 8 of pregnancy, corpora lutea on days 8 and 12 had regressed and serum progesterone (P) levels were less than 2 ng/ml. However, serum estradiol levels and the number of antral follicles (AF) were not different from NHS controls. There were approximately 11 AF/ovary and 17 AF/ovary in the days 4 and 8 groups, respectively; 4–9 days after ALH, spontaneous superovulation of 23 ± 3 (day 4 group) and 29 ± 4 (day 8 group) ova was observed. In contrast, the rat ovulates only 12.5 ± 0.3 (n = 11) ova after injection of the same ALH (0.2 or 0.5 ml) on day 8 of pregnancy. Serum levels of FSHlike material in ALH-treated hamsters were extremely elevated (3.0 μg/ml) when compared to NHS controls (250 ng/ml). Pregnant hamsters were injected with ALH or NHS and ovariectomized (OVX) on day 8. Within 24 h after OVX, serum levels of FSH-like material were approximately 3.5 μg/ml in ALH-treated hamsters (1.0 μg FSH/ml in NHS controls), and FSH remained elevated for at least 4 days. The extremely elevated levels of FSH-like material in serum of ALH-treated hamsters were probably due to several factors: 1) removal of steroid negative feedback at the hypothalamic-pituitary axis; 2) removal of any nonsteroidal, (folliculostatin) negative feedback; and 3) interference of ALH in the rat FSH RIA. A transient increase in serum LH was also observed in NHS OVX controls. Thus, 4 days after ALH treatment, estradiol levels and antral follicular development appeared to keep pace with the values of pregnant controls by hypersecretion of gonadotropins (FSH and probably LH). To determine the minimum steroid requirement for prevention of ALH-induced interruption of pregnancy, hamsters injected with ALH on days 4 or 8 were administered a daily steroid regimen and autopsied 4 days later. P alone reversed the abortifacient effects of ALH. Less P was required for pregnancy maintenance on days 4–8 (50 μg/day) than on days 8–12 (250 μg/day). A subminimal dose of P (100 μg/day) combined with 1 jug estradiol cyclopentylpropionate (ECP) twice daily on days 8–12 maintained pregnancy. The potentiating effect of ECP was not observed on days 4–8, although 50 fig P and 1 μg ECP/day increased uterine-swelling weights. The abortifacient effect of ALH on day 8 could not be reversed by daily administration of 1 mg testosterone propionate, contrary to what has been reported for rats